Found the problem.
My items have underscores in the names.
e.g. "VENDOR_CV"
Using a search term that includes an underscore produces no results.
However, if I replace the underscore with a space, then the object is found.
Search Term "VENDOR_CV" produces no results.
Search Term "VENDOR CV" does find the item.
Something you can work around once you know - but not ideal .